Optical waveguide structure

Abstract

An optical waveguide structure according to the invention comprises a core layer having a first refractive index n core , an array of sub-regions within the core having a second refractive index n rods , the array of sub-regions giving rise to a photonic band structure within the core layer, and a cladding layer adjacent to the core layer having a refractive index n cladding , wherein: n core >n rods ≧n cladding , The structure of the present invention is less lossy than prior waveguide structures having photonic bandstructure regions. The out of plane divergence of light in the sub-regions is reduced as compared with air holes which are typically used in photonic crystal structures. As a result more light is coupled back into the core at the sub-region/core interface. Coupling of light into the buffer layer is also reduced. Furthermore, there are added advantages over the prior art associated with the fabrication of these structures.

1 . An optical waveguide structure comprising a core layer having a first refractive index n core , an array of sub-regions within the core having a second refractive index n rods , the array of sub-regions giving rise to a photonic band structure experienced by an optical mode travelling through the waveguide structure, and a cladding layer adjacent to the core layer having a refractive index n cladding , wherein:  
       n core >n rods ≧n cladding .  
     
     
         2 . An optical waveguide structure according to  claim 1 , wherein the array of sub-regions gives rise to a photonic bandgap.  
     
     
         3 . An optical waveguide structure according to  claim 1 , wherein the waveguide structure is a planar waveguide structure further including a buffer layer having a refractive index n buffer , wherein the core layer is positioned between the buffer layer and the cladding layer and wherein:  
       n core >n rods ≧n buffer .  
     
     
         4 . An optical waveguide structure according to  claim 1 , wherein the waveguide structure is an optical fibre structure, the cladding layer surrounding the core layer.  
     
     
         5 . An optical waveguide structure according to  claim 1 , wherein the core layer has a refractive index between 1.4 and 4.  
     
     
         6 . An optical waveguide structure according to  claim 1 , wherein the sub-regions have a refractive index between 1.3 and 1.6.  
     
     
         7 . An optical waveguide structure according to  claim 1 , wherein the cladding layer has a refractive index between 1.3 and 1.6.  
     
     
         8 . An optical waveguide structure according to  claim 3 , wherein the buffer layer has a refractive index between 1.3 and 1.6.  
     
     
         9 . An optical waveguide structure according to  claim 1 , wherein the sub-regions are formed from silicon oxynitride or silicon dioxide.  
     
     
         10 . An optical waveguide structure according to  claim 1 , wherein the core layer is formed from silicon nitride, doped silica, tantalum pentoxide or doped tantalum pentoxide.  
     
     
         11 . An optical waveguide structure according to  claim 1 , wherein the cladding layer is formed from silicon dioxide.  
     
     
         12 . An optical waveguide structure according to  claim 3 , wherein the buffer layer is formed from silicon dioxide.  
     
     
         13 . An optical waveguide structure according to  claim 1 , wherein the sub-regions extend through the cladding layer as well as the core layer.  
     
     
         14 . An optical waveguide structure according to  claim 3 , wherein the sub-regions extend partially or fully into the buffer layer.  
     
     
         15 . An optical waveguide structure according to  claim 1 , wherein the cladding layer includes sub-regions corresponding to the sub-regions in the core layer having a refractive index which is greater than or equal to the refractive index of the cladding layer but which is less than or equal to the refractive index of the sub-regions in the core.  
     
     
         16 . An optical waveguide structure according to  claim 1 , wherein the core layer includes a lateral waveguiding region having no sub-regions.  
     
     
         17 . An optical waveguide structure according to  claim 16 , wherein the waveguiding region includes a waveguide bend.  
     
     
         18 . An optical device including an optical waveguide structure according to  claim 1 .  
     
     
         19 . A method of manufacturing a optical waveguide structure comprising the steps of: 
 providing a core layer having a first refractive index n core ;    providing an array of sub-regions within the core having a second refractive index n rods , the array of sub-regions giving rise to a photonic band structure experienced by an optical mode travelling through the waveguide structure; and    providing a cladding layer adjacent to the core layer having a refractive index n cladding ; wherein:    n core >n rods ≧n cladding .    
     
     
         20 . A method according to  claim 19 , wherein the optical waveguide is planar, the method further including the step of providing a buffer layer having a refractive index n buffer  on the opposite side of the core layer to the cladding layer, wherein:  
       n core >n rods ≧n buffer .  
     
     
         21 . A method according to  claim 19 , wherein the optical waveguide is an optical fibre, the method further including the steps of: 
 providing the cladding layer surrounding the core layer.    
     
     
         22 . A method of guiding an optical signal comprises the step of passing an optical signal through a waveguiding region of an optical waveguide structure comprising a core layer having a first refractive index n core , an array of sub-regions within the core layer having a second refractive index n rods , the array of sub-regions giving rise to a photonic band structure experienced by an optical mode travelling through the waveguide structure, and a cladding layer adjacent the core layer having a refractive index n cladding , wherein:  
       n core >n rods ≧n cladding .  
     
     
         23 . A method according to  claim 22 , wherein the optical waveguide structure is a planar structure, further including a buffer layer having a refractive index n buffer , wherein the core layer is positioned between the buffer layer and the cladding layer and wherein:  
       n core >n rods ≧n buffer .  
     
     
         24 . A method according to  claim 22 , wherein the waveguide structure is an optical fibre structure, wherein the cladding layer surrounds the core layer.